NK1- and NK3-receptor mediated inhibition of 5-hydroxytryptamine release from the vascularly perfused small intestine of the guinea-pig

Abstract

The effects of tachykinins on the spontaneous release of 5-hydroxytryptamine (5-HT) from the enterochromaffin cells into the portal circulation was investigated in vitro using the vascularly perfused isolated guinea-pig small intestine. 5-HT was determined by HPLC with electrochemical detection. Test substances were applied intraarterially. Substance P (SP) caused a concentration-dependent decrease in 5-HT outflow with an EC50 of 50 pmol/l. Similarly, the selective NK1 receptor agonist SP methyl ester (1 nmol/l) significantly inhibited 5-HT outflow (to 51 +/- 3%). When tetrodotoxin (1 mumol/l) was added to the arterial perfusion medium, the inhibition by SP of 5-HT outflow was not affected. The selective NK1 receptor antagonist CP 99994 [(+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine] (0.1 mumol/l) prevented the inhibitory effect of SP (0.1 mumol/l). Neither GR 94800 (PhCO-Ala-Ala-DTrp-Phe-DPro-Pro-NleNH2) (0.1 mumol/l) nor SR 142801 [(S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl) piperidin-3-yl)propyl)-4-phenylpiperidin-4-yl)-N- methylacetamide] (10 nmol/l), which are selective NK2 and NK3 receptor antagonists, changed the SP-mediated inhibition. The selektive NK3 receptor agonist senktide (10 nmol/l) also decreased the 5-HT outflow (to 57 +/- 5%). This inhibition was prevented by SR 142801 (10 nmol/l) and by tetrodotoxin. CP 99994 (0.1 mumol/l) significantly antagonized the senktide-mediated inhibition of 5-HT outflow. The outflow of 5-HT was unaffected when CP 99994, GR 94800 or SR 142801 alone were added to the perfusion medium. It is concluded that the release of 5-HT from enterochromaffin cells is directly inhibited by NK1 receptors, and indirectly by neuronal NK3 receptors whose stimulation leads to the release of SP.

Involvement of substance P in the development of cisplatin‐induced acute and delayed pica in rats

“…Previous studies have demonstrated that cisplatin may induce SP synthesis in the mucosa of the GI tract, and NK 1 receptor antagonists modulate visceral efferent functions (Greenwood‐Van Meerveld et al ., ; Qian et al ., ). Furthermore, there is evidence to suggest that SP via NK 1 receptors enhances the release of 5‐HT from EC cells (Ginap and Kilbinger, ). Thus, it is possible that the therapeutic effects of 5‐HT 3 receptor antagonists on the acute phase of cisplatin‐induced emesis are potentially and partially mediated by peripheral NK 1 receptors.…”

High Mucosal Serotonin Availability in Neonatal Guinea Pig Ileum Is Associated With Low Serotonin Transporter Expression

“…3,20,21 In order elicit release of detectable amounts of 5-HT, large volume samples and prolonged periods of pharmacological or electrical stimulation were required. While these studies have provided important data about EC cell function, overflow techniques do not allow 5-HT measurements in real time and they have poor spatial resolution as the molecule is released from many hundreds of EC cells from extended lengths of intestine.…”

Evidence for a Re-Evaluation of the Neurochemical and Anatomical Bases of Chemotherapy-Induced Vomiting

“…Immunohistochemical labeling in the nucleus of the solitary tract demonstrated punctate, terminal-like labeling for 5-HT and SP, both separately and colocalized, suggesting that the NK 1 and 5-HT 3 receptors could be activated simultaneously or individually during chemotherapy-induced vomiting. In the gastrointestinal tract, SP-immunoreactive fibers project from the submucosal nerve plexus to close apposition with NK 1 receptor- and 5-HT-containing enterochromaffin cells (Ray, Chebolu, and Darmani, unpublished data), and rare colocalization of 5-HT- and SP-immunoreactive neurons have also been noted . SP is not limited to 5-HT in its interactions, however, in that it interacts with dopaminergic systems as well.…”